Optical Imaging: A New Window to the Adult Brain

Abstract

Noninvasive optical imaging is an emerging method of functional neuroimaging that has major advantages that make it particularly suited to both basic and clinical neuroscience research as well as to clinical practice. [2][3][4][5][6][7] It has great promise for contributing to neuropsychiatry. 2 The required equipment is compact and portable, it is relatively easy to use, and the method is relatively tolerant of subject movement. Studies can be performed in almost any location including at the bedside and in natural settings. Patients who are not good candidates for more traditional functional imaging methods (e.g., functional MRI [fMRI] and positron emission tomography [PET]) often do well with optical imaging, as it does not require absolute stillness or confinement and has no associated loud noises. It is also safe to use in the presence of metal (e.g., plates, pins, pacemakers), an important consideration for some populations of interest. It has much faster time resolution than most other functional imaging techniques and can easily provide repeated within-subject measures. Other major advantages are low cost and high safety. Like surface electroencephalography (EEG), optical imaging captures activation-related changes only from the cerebral cortex. Historically, the major disadvantages of optical imaging have been its lower spatial resolution and smaller regions of coverage, areas of major improvement over the last decade. Use of optical imaging for monitoring of cerebral state in high-risk situations (e.g., neurosurgery, intensive care unit), while an important clinical application, is outside the scope of this review. [8][9][10] The concept that the functional state of tissue influences its optical properties in observable ways is well accepted. Familiar medical examples include hypoxia-induced cyanosis and anemia-related pallor. Both result from changes in the concentration of oxyhemoglobin (HbO2) and deoxyhemoglobin (HbR). Hemoglobin (Hb) is a chromophore, a chemical group that absorbs light at a specific frequency, thus imparting coloration. Most noninvasive optical neuroimaging approaches presently used in clinical practice and human research are based on using some version of near-infrared spectroscopy (NIRS) to measure intrinsic activation-related changes in the concentrations of oxyhemoglobin and deoxyhemoglobin. Thus, similar to fMRI, optical neuroimaging measures the hemodynamic response to brain

In Vivo Analysis of a Biodegradable Magnesium Alloy Implant in an Animal Model Using Near-Infrared Spectroscopy

“…The NIR range strongly influences absorption due to hemoglobin and cytochrome C oxidase. Oxyhemoglobin absorption rises, while deoxyhemoglobin reduces below 800 nm, and metabolism-related changes (cytochrome C oxidase) peak at around 800 nm [ 31 , 40 , 41 , 42 ]. The region above 940 nm hints at water content in the tissues.…”

“…Hence, we believe this abnormal skin rash influenced the optical measurements and might justify the significant difference near 955 nm compared to rats 3 and 4, as highlighted in Figure 6 . Therefore, we hypothesized that the derivative spectra, particularly in the 700–900 nm range collected from rat 1 and rat 2, indicated changes in hemoglobin and cell metabolism at the wound site that correlated with outcomes not associated with the successful progression of healing (reference to Figure 2 in [ 31 ]). Optical data depend on local tissue [ 33 ].…”

“…In vivo data collection used a probe light source–detector separation of 8.0 mm. As a rule of thumb, the measurements were expected to be from a depth equal to around 1/2 to 1/3 of the source–detector distance [ 30 , 31 ]. The experiment with the optical probe showed a 100% difference in the PCA score plot of the data collected from 6 mm and 8 mm source–detector distances [ 21 ].…”

“…Different layers, such as fat, skin, muscles, and blood flow, influence the in vivo optical data from animals. The fat scatters light, while hemoglobin in the blood absorbs NIR light [ 31 , 34 , 35 ]. Due to the degradation of magnesium-based implants, there are complex chemical reactions near the implants, including changes in pH [ 15 , 25 ].…”

Possible neural mechanisms of psychotherapy for trauma-related symptoms: cerebral responses to the neuropsychological treatment of post-traumatic stress disorder model individuals

“…Regional cerebral blood flow was measured in terms of changes in [oxy-Hb] and deoxygenated haemoglobin ([deoxy-Hb]) levels. In this study, changes in [oxy-Hb] levels, the most sensitive indicator of changes in regional cerebral blood flow, were used as the index of activation 59 . The baseline [oxy-Hb] level was the average value during the last 5 s of the 5-min rest period after placing the probes on the head.…”